fs/afs/security.c

   1 /* AFS security handling
   2  *
   3  * Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/init.h>
  13 #include <linux/slab.h>
  14 #include <linux/fs.h>
  15 #include <linux/ctype.h>
  16 #include <linux/sched.h>
  17 #include <linux/hashtable.h>
  18 #include <keys/rxrpc-type.h>
  19 #include "internal.h"
  20
  21 static DEFINE_HASHTABLE(afs_permits_cache, 10);
  22 static DEFINE_SPINLOCK(afs_permits_lock);
  23
  24 /*
  25  * get a key
  26  */
  27 struct key *afs_request_key(struct afs_cell *cell)
  28 {
  29         struct key *key;
  30
  31         _enter("{%x}", key_serial(cell->anonymous_key));
  32
  33         _debug("key %s", cell->anonymous_key->description);
  34         key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
  35                           NULL);
  36         if (IS_ERR(key)) {
  37                 if (PTR_ERR(key) != -ENOKEY) {
  38                         _leave(" = %ld", PTR_ERR(key));
  39                         return key;
  40                 }
  41
  42                 /* act as anonymous user */
  43                 _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
  44                 return key_get(cell->anonymous_key);
  45         } else {
  46                 /* act as authorised user */
  47                 _leave(" = {%x} [auth]", key_serial(key));
  48                 return key;
  49         }
  50 }
  51
  52 /*
  53  * Dispose of a list of permits.
  54  */
  55 static void afs_permits_rcu(struct rcu_head *rcu)
  56 {
  57         struct afs_permits *permits =
  58                 container_of(rcu, struct afs_permits, rcu);
  59         int i;
  60
  61         for (i = 0; i < permits->nr_permits; i++)
  62                 key_put(permits->permits[i].key);
  63         kfree(permits);
  64 }
  65
  66 /*
  67  * Discard a permission cache.
  68  */
  69 void afs_put_permits(struct afs_permits *permits)
  70 {
  71         if (permits && refcount_dec_and_test(&permits->usage)) {
  72                 spin_lock(&afs_permits_lock);
  73                 hash_del_rcu(&permits->hash_node);
  74                 spin_unlock(&afs_permits_lock);
  75                 call_rcu(&permits->rcu, afs_permits_rcu);
  76         }
  77 }
  78
  79 /*
  80  * Clear a permit cache on callback break.
  81  */
  82 void afs_clear_permits(struct afs_vnode *vnode)
  83 {
  84         struct afs_permits *permits;
  85
  86         spin_lock(&vnode->lock);
  87         permits = rcu_dereference_protected(vnode->permit_cache,
  88                                             lockdep_is_held(&vnode->lock));
  89         RCU_INIT_POINTER(vnode->permit_cache, NULL);
  90         vnode->cb_break++;
  91         spin_unlock(&vnode->lock);
  92
  93         if (permits)
  94                 afs_put_permits(permits);
  95 }
  96
  97 /*
  98  * Hash a list of permits.  Use simple addition to make it easy to add an extra
  99  * one at an as-yet indeterminate position in the list.
 100  */
 101 static void afs_hash_permits(struct afs_permits *permits)
 102 {
 103         unsigned long h = permits->nr_permits;
 104         int i;
 105
 106         for (i = 0; i < permits->nr_permits; i++) {
 107                 h += (unsigned long)permits->permits[i].key / sizeof(void *);
 108                 h += permits->permits[i].access;
 109         }
 110
 111         permits->h = h;
 112 }
 113
 114 /*
 115  * Cache the CallerAccess result obtained from doing a fileserver operation
 116  * that returned a vnode status for a particular key.  If a callback break
 117  * occurs whilst the operation was in progress then we have to ditch the cache
 118  * as the ACL *may* have changed.
 119  */
 120 void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 121                       unsigned int cb_break)
 122 {
 123         struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
 124         afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
 125         size_t size = 0;
 126         bool changed = false;
 127         int i, j;
 128
 129         _enter("{%llx:%llu},%x,%x",
 130                vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
 131
 132         rcu_read_lock();
 133
 134         /* Check for the common case first: We got back the same access as last
 135          * time we tried and already have it recorded.
 136          */
 137         permits = rcu_dereference(vnode->permit_cache);
 138         if (permits) {
 139                 if (!permits->invalidated) {
 140                         for (i = 0; i < permits->nr_permits; i++) {
 141                                 if (permits->permits[i].key < key)
 142                                         continue;
 143                                 if (permits->permits[i].key > key)
 144                                         break;
 145                                 if (permits->permits[i].access != caller_access) {
 146                                         changed = true;
 147                                         break;
 148                                 }
 149
 150                                 if (afs_cb_is_broken(cb_break, vnode,
 151                                                      vnode->cb_interest)) {
 152                                         changed = true;
 153                                         break;
 154                                 }
 155
 156                                 /* The cache is still good. */
 157                                 rcu_read_unlock();
 158                                 return;
 159                         }
 160                 }
 161
 162                 changed |= permits->invalidated;
 163                 size = permits->nr_permits;
 164
 165                 /* If this set of permits is now wrong, clear the permits
 166                  * pointer so that no one tries to use the stale information.
 167                  */
 168                 if (changed) {
 169                         spin_lock(&vnode->lock);
 170                         if (permits != rcu_access_pointer(vnode->permit_cache))
 171                                 goto someone_else_changed_it_unlock;
 172                         RCU_INIT_POINTER(vnode->permit_cache, NULL);
 173                         spin_unlock(&vnode->lock);
 174
 175                         afs_put_permits(permits);
 176                         permits = NULL;
 177                         size = 0;
 178                 }
 179         }
 180
 181         if (afs_cb_is_broken(cb_break, vnode, vnode->cb_interest))
 182                 goto someone_else_changed_it;
 183
 184         /* We need a ref on any permits list we want to copy as we'll have to
 185          * drop the lock to do memory allocation.
 186          */
 187         if (permits && !refcount_inc_not_zero(&permits->usage))
 188                 goto someone_else_changed_it;
 189
 190         rcu_read_unlock();
 191
 192         /* Speculatively create a new list with the revised permission set.  We
 193          * discard this if we find an extant match already in the hash, but
 194          * it's easier to compare with memcmp this way.
 195          *
 196          * We fill in the key pointers at this time, but we don't get the refs
 197          * yet.
 198          */
 199         size++;
 200         new = kzalloc(sizeof(struct afs_permits) +
 201                       sizeof(struct afs_permit) * size, GFP_NOFS);
 202         if (!new)
 203                 goto out_put;
 204
 205         refcount_set(&new->usage, 1);
 206         new->nr_permits = size;
 207         i = j = 0;
 208         if (permits) {
 209                 for (i = 0; i < permits->nr_permits; i++) {
 210                         if (j == i && permits->permits[i].key > key) {
 211                                 new->permits[j].key = key;
 212                                 new->permits[j].access = caller_access;
 213                                 j++;
 214                         }
 215                         new->permits[j].key = permits->permits[i].key;
 216                         new->permits[j].access = permits->permits[i].access;
 217                         j++;
 218                 }
 219         }
 220
 221         if (j == i) {
 222                 new->permits[j].key = key;
 223                 new->permits[j].access = caller_access;
 224         }
 225
 226         afs_hash_permits(new);
 227
 228         /* Now see if the permit list we want is actually already available */
 229         spin_lock(&afs_permits_lock);
 230
 231         hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
 232                 if (xpermits->h != new->h ||
 233                     xpermits->invalidated ||
 234                     xpermits->nr_permits != new->nr_permits ||
 235                     memcmp(xpermits->permits, new->permits,
 236                            new->nr_permits * sizeof(struct afs_permit)) != 0)
 237                         continue;
 238
 239                 if (refcount_inc_not_zero(&xpermits->usage)) {
 240                         replacement = xpermits;
 241                         goto found;
 242                 }
 243
 244                 break;
 245         }
 246
 247         for (i = 0; i < new->nr_permits; i++)
 248                 key_get(new->permits[i].key);
 249         hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
 250         replacement = new;
 251         new = NULL;
 252
 253 found:
 254         spin_unlock(&afs_permits_lock);
 255
 256         kfree(new);
 257
 258         spin_lock(&vnode->lock);
 259         zap = rcu_access_pointer(vnode->permit_cache);
 260         if (!afs_cb_is_broken(cb_break, vnode, vnode->cb_interest) &&
 261             zap == permits)
 262                 rcu_assign_pointer(vnode->permit_cache, replacement);
 263         else
 264                 zap = replacement;
 265         spin_unlock(&vnode->lock);
 266         afs_put_permits(zap);
 267 out_put:
 268         afs_put_permits(permits);
 269         return;
 270
 271 someone_else_changed_it_unlock:
 272         spin_unlock(&vnode->lock);
 273 someone_else_changed_it:
 274         /* Someone else changed the cache under us - don't recheck at this
 275          * time.
 276          */
 277         rcu_read_unlock();
 278         return;
 279 }
 280
 281 /*
 282  * check with the fileserver to see if the directory or parent directory is
 283  * permitted to be accessed with this authorisation, and if so, what access it
 284  * is granted
 285  */
 286 int afs_check_permit(struct afs_vnode *vnode, struct key *key,
 287                      afs_access_t *_access)
 288 {
 289         struct afs_permits *permits;
 290         bool valid = false;
 291         int i, ret;
 292
 293         _enter("{%llx:%llu},%x",
 294                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 295
 296         /* check the permits to see if we've got one yet */
 297         if (key == vnode->volume->cell->anonymous_key) {
 298                 _debug("anon");
 299                 *_access = vnode->status.anon_access;
 300                 valid = true;
 301         } else {
 302                 rcu_read_lock();
 303                 permits = rcu_dereference(vnode->permit_cache);
 304                 if (permits) {
 305                         for (i = 0; i < permits->nr_permits; i++) {
 306                                 if (permits->permits[i].key < key)
 307                                         continue;
 308                                 if (permits->permits[i].key > key)
 309                                         break;
 310
 311                                 *_access = permits->permits[i].access;
 312                                 valid = !permits->invalidated;
 313                                 break;
 314                         }
 315                 }
 316                 rcu_read_unlock();
 317         }
 318
 319         if (!valid) {
 320                 /* Check the status on the file we're actually interested in
 321                  * (the post-processing will cache the result).
 322                  */
 323                 _debug("no valid permit");
 324
 325                 ret = afs_fetch_status(vnode, key, false);
 326                 if (ret < 0) {
 327                         *_access = 0;
 328                         _leave(" = %d", ret);
 329                         return ret;
 330                 }
 331                 *_access = vnode->status.caller_access;
 332         }
 333
 334         _leave(" = 0 [access %x]", *_access);
 335         return 0;
 336 }
 337
 338 /*
 339  * check the permissions on an AFS file
 340  * - AFS ACLs are attached to directories only, and a file is controlled by its
 341  *   parent directory's ACL
 342  */
 343 int afs_permission(struct inode *inode, int mask)
 344 {
 345         struct afs_vnode *vnode = AFS_FS_I(inode);
 346         afs_access_t uninitialized_var(access);
 347         struct key *key;
 348         int ret;
 349
 350         if (mask & MAY_NOT_BLOCK)
 351                 return -ECHILD;
 352
 353         _enter("{{%llx:%llu},%lx},%x,",
 354                vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
 355
 356         key = afs_request_key(vnode->volume->cell);
 357         if (IS_ERR(key)) {
 358                 _leave(" = %ld [key]", PTR_ERR(key));
 359                 return PTR_ERR(key);
 360         }
 361
 362         ret = afs_validate(vnode, key);
 363         if (ret < 0)
 364                 goto error;
 365
 366         /* check the permits to see if we've got one yet */
 367         ret = afs_check_permit(vnode, key, &access);
 368         if (ret < 0)
 369                 goto error;
 370
 371         /* interpret the access mask */
 372         _debug("REQ %x ACC %x on %s",
 373                mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
 374
 375         if (S_ISDIR(inode->i_mode)) {
 376                 if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
 377                         if (!(access & AFS_ACE_LOOKUP))
 378                                 goto permission_denied;
 379                 }
 380                 if (mask & MAY_WRITE) {
 381                         if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
 382                                         AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
 383                                 goto permission_denied;
 384                 }
 385         } else {
 386                 if (!(access & AFS_ACE_LOOKUP))
 387                         goto permission_denied;
 388                 if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
 389                         goto permission_denied;
 390                 if (mask & (MAY_EXEC | MAY_READ)) {
 391                         if (!(access & AFS_ACE_READ))
 392                                 goto permission_denied;
 393                         if (!(inode->i_mode & S_IRUSR))
 394                                 goto permission_denied;
 395                 } else if (mask & MAY_WRITE) {
 396                         if (!(access & AFS_ACE_WRITE))
 397                                 goto permission_denied;
 398                         if (!(inode->i_mode & S_IWUSR))
 399                                 goto permission_denied;
 400                 }
 401         }
 402
 403         key_put(key);
 404         _leave(" = %d", ret);
 405         return ret;
 406
 407 permission_denied:
 408         ret = -EACCES;
 409 error:
 410         key_put(key);
 411         _leave(" = %d", ret);
 412         return ret;
 413 }
 414
 415 void __exit afs_clean_up_permit_cache(void)
 416 {
 417         int i;
 418
 419         for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
 420                 WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
 421
 422 }